This invention relates to a nozzle for an injection molding machine for simultaneously injecting at least two plasticized materials into the mold of the machine.
Such injection nozzles are provided to either produce multicolored injection molded plastic articles wherein, depending on the process sequence, more or less continuous transitions from one color to another are desired, or to produce injection molded plastic articles with one or more layers, such as an inexpensive core layer and a more costly and attractive surface layer or layers.
Such nozzles are generally disclosed in French patent 1290262, and in German patents 2342789, 2346135 and 2445112. As disclosed therein, the feed channels within each nozzle are directed coaxially at least at the terminal portion of their path to a joint nozzle outlet, where separate valves for each channel are arranged either before reaching the coaxial channel guide in each channel, or are formed by the moveable channel guide elements themselves. These known constructions appear to permit a compact construction of the nozzles, but basically require that the channels within a nozzle have a plurality of bends, because of the desired compactness and because of the minimum spacing between the nozzle inlet specified by the dimensions of the plasticizing units.
Each such bend in flow of plasticized material, however, produces an additional resistance for the plasticized flow property, which plasticized material is connected by a suitable power supply to the conveying device coupled to the plasticizing unit for the particular plastic component. For injection molding machines developed for very large and complicated plastic bodies and which operate with considerable injection pressures, a minimizing of the injection molding intervals to increase product output and produce energy savings would result in noticable cost savings and significantly reduce the environmental impact.
German patent 2705291 dispenses with the nozzle totally, and instead couples the outlet of the plasticizing units directly to a corresponding number of individual inlets of the sprue bushing of the injection molding machine that is embedded in the thermoforming mold and that has only one common outlet for all plastic components with respect to the mold. If necessary, between the plasticizing units and the sprue bushing a nozzle head is provided that apparently contains only individual connecting channels between the plasticizing units and the individual inlets of the sprue bushing. However, the use of one of the aforedescribed arrangements exhibits the drawback that the sprue formed automatically during the production of the molded parts has in the direction of the molded part a relatively large cross section which can be flawlessly removed from the finished molded part only with a great deal of technical complexity and thus also additional cost and additional energy.
European published application 0311875 discloses the use of a sprue bushing which tapers off on the side of the mold to narrow outlet openings, although the flows of plasticized materials are fed first into the lateral cavities which must decelerate and divert the respective flow. In principle, however, the result has the same effect as the aforementioned bent flow channel guides within a nozzle.